Mainframe computing is a computing platform used today by the largest companies in the world. A mainframe often processes many workloads such as accounts receivable, general ledger, payroll and a variety of applications needed for specific business requirements. These workloads are commonly referred to as jobs.
A mainframe is a complex environment consisting of databases and datasets (i.e., files). These data typically reside on a direct access storage device (DASD) or disk drive. In addition to DASD, mainframe applications also rely on one or more tape drives/devices to store portions of these data. Tape drive(s) can be the primary repository of vital information within a mainframe application. Tape today can be either physical tape which must be mounted on hardware to be read or virtual tape which is disk-based storage emulating physical tape.
Mainframe computers process information in one of two modes of operation, online or batch. An online system, for example, provides an interactive application interface for interaction by customers and employees. In contrast, a batch system, for example, involves non-interactive processing of an application (e.g., generating statements) in which the application is started and runs without intervention until it completes. Both batch and online applications exist and run in predetermined cycles to automate data processing for an organization.
Replication is the process of creating an exact copy of a particular storage system, either DASD or tape. In replicated batch environments, multiple devices (e.g., primary storage system and replicated storage system) are generally kept to a certain consistency point. That is, the data on the primary storage system is timed at the same exact point on the replicated storage system. A consistency group is a collection of storage to be maintained in a consistent state (e.g., consistency group A includes volume A and tape drive 1, consistency group B includes volumes B and C).
While replication occurs at a point in time, data processing typically doesn't stop at that point in time during the replication. Furthermore, replication, especially when tape-based storage systems are involved, requires processing time, even if nominal, to create the copy. Thus, the replicated copy, by its very nature, may already be outdated at the point in time of the replication.
In addition, a particular mainframe application may utilize various datasets stored across various primary storage systems that may include both DASD and tape. Replication is performed, for example, for each individual storage system. As such, replication of each of the various datasets utilized by the particular mainframe application may occur at different times.